ITU-T defines an Optical Transport Network (OTN) as a set of optical elements that are connected by optical links and that are capable of providing transporting, multiplexing, switching, management, and supervision functionality and survivability of optical channels carrying client signals.
OTN uses digital wrapper technology that provides a method for encapsulating data in a frame, or optical data unit. Generally, digital wrapping involves grouping a number of existing frames together into one entity that can be more efficiently managed with a small allocation of overhead and forward error correction (FEC) bytes. There are three levels of hierarchy for the encapsulation: the optical channel payload unit (OPUk) for encapsulation of client data; the optical channel data unit (ODUk) for encapsulating the OPUk data; and the optical channel transport unit (OTUk) for encapsulating the ODUk data.
The OTN standard provides a method for adding management and intelligence to optical carriers, specifically wavelengths in DWDM systems. This methodology involves wrapping client information of any protocol in a frame carrying information about both the client and the optical carrier. The information can then be used to manage the optical signals.